1. Field of the Invention
The present invention relates to methods of cementing subterranean zones using cement compositions containing biodegradable dispersants.
2. Description of the Prior Art
In the cementing of oil and gas wells and the like, dispersants are extensively used to reduce the rheologies of cement compositions, i.e., the apparent viscosities and other properties of the cement compositions, as well as to reduce the water content of the cement compositions. The reduction of the rheology of a cement composition allows the cement composition to be pumped with less friction pressure which utilizes less pump horsepower. In addition, the lower rheology often allows the cement composition to be pumped in turbulent flow. Turbulent flow characteristics are desirable when pumping cement compositions in oil and gas wells to more efficiently remove drilling fluid from surfaces in the well bore as the drilling fluid is displaced by the cement composition being pumped. The inclusion of dispersants in cement compositions is also desirable in that the presence of the dispersants reduces the water required for preparation of the cement compositions. Cement compositions having reduced water content are characterized by improved compressive strength development.
A number of dispersing agents have been utilized heretofore in cement compositions, particularly in cement compositions used for primary and remedial cementing in oil and gas wells. For example, certain organic acids such as gluconic acid and citric acid have been recognized by those skilled in the art as cement dispersants. However, such organic acids are also strong cement composition set retarding agents which is often undesirable. That is, the presence of an organic acid dispersant in a cement composition prevents the cement composition from setting for a relatively long period of time which is often costly or otherwise detrimental. Other dispersants which are commonly used in hydraulic cement compositions include polynapthylene sulfonate which is commercially available under the trade designation “CFR-2™” from Halliburton Energy Services of Duncan, Okla., the condensation product of formaldehyde, acetone and a sulfite which is commercially available under the trade designation “CFR-3™” from Halliburton Energy Services, poly-B-naphthol sulfonate, polymelamine sulfonate and many others. Another highly efficient dispersant for use in cement compositions is disclosed in U.S. Pat. No. 6,136,950 issued to Vickers, Jr. et al. on Oct. 24, 2000 which is incorporated herein by reference. The dispersant is a polycarboxylate polymer comprised of a functionalized polyamide main chain polymer onto which are grafted at least some oligomeric or polymeric hydrophilic side chains. Commercially available dispersants are generally not environmentally acceptable, especially in offshore operations, in that they do not undergo complete biodegradation in the environment and can cause damage to aquatic and other life therein.
Thus, there are needs for improved methods of cementing subterranean zones penetrated by well bores using cement compositions containing biodegradable dispersants.